JPS5843610A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To elevate the characteristics, by compensating deterioration of the characteristics due to a diffraction effect in case when a side lobe of a transducer has been formed at a position deviated in the vertical direction against the propagating direction of a surface acoustic wave from a main lobe. CONSTITUTION:Against a beam center axis L1 of a surface acoustic wave energized from a main lobe A of the first transducer 11, a cross center axis L2 of a normal type interdigital electrode for constituting the second transducer 12 is deviated by a distance of WL/2 vertically against the propagating direction of the surface acoustic wave, and also in the direction of a position of a side lobe C. In this way, the surface acoustic wave energized from the main lobe A and the side lobe B is received satisfactorily by the second transducer 12, also is energized from the side lobe C being an energizing source, which is far from a point where the surface acoustic wave reaches, is subjected to large diffraction as indicated with an arrow D, and the surface acoustic wave expanded to the outside and propagated is also nearly received by the transducer 12, therefore, deterioration of the characteristics caused by a diffraction effect can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generates surface acoustic waves using a transducer made of interdigital electrodes subjected to apodice weighting and a transducer made of regular interdigital electrodes.

Surface acoustic wave devices are generally elastic! ! ! Electrical signal for excitation of C21 elastically damped plane waves on a substrate made of piezoelectric material that propagates plane waves - person who operates a surface acoustic wave device, output transducer -
* Form and compose.

For these input, output, and output transducers, interdigital electrodes are usually used in which a pair of comb-like electrodes are crossed or interdigitated with each other.

Here, interdigital electrodes with a uniform crossing length (the length at which a pair of comb-shaped electrodes interlock with each other) are called regular type interdigital electrodes, or are composed of two such regular type interdigital electrodes. The transducer is

(1111 Logarithm 4=Therefore, the passband characteristics are uniquely determined.

In the case of constructing a filter system, in order to obtain the desired same wave number characteristic, the intersection length of the interdigital electrodes is degraded at the position 1 in the surface acoustic wave propagation direction. A weighting process called an all die (p*d1ms) is applied.

No. 1111 shows the structure of a conventional elastic graphite wave filter applying this piezoelectric technology.
, , ,F22. ．． 1□,,□5. Yo6: □.

The first one was all about form and power. 8th trans day tool - Zudea D s
The transducer 11 of IE) is constituted by an apodized interdigital electrode 2. The second transducer 12 is constituted by a regular type interdigital electrode I.

In this case, for example, the first transducer 11 is used as an input transducer for converting the electrical signal 4i elastic surface i4=', and the second transducer 12 is It is used as an output transducer to convert the excited acoustic wave into an electrical signal.

□ Here, the intersecting areas of the interdigital electrodes constituting the first transducer 11 are shown by broken lines, and the large intersecting area at the center of these holes is called the main opening. The relatively small intersecting regions B and 0 of ゛ are called side lobes, and the surface acoustic waves are excited from these main lobes and side lobes B and 0. In FIG. 1, the main loop and the side loops B and 6 are all arranged so that the beam center axes of the surface acoustic waves excited therefrom coincide with each other. In the case of this structure 1 For example, V a B (Vi
sliiglml 8th e Ban, d,) and -m
If you try to create a small % 11 high performance elastic paper wave filter for APS FAST/T, it will be a bullet! ! IA! Due to the phase distortion and re-excitation effect of the first pass, characteristic deterioration such as rounded shoulders in the first passing region occurs, making it impossible to obtain satisfactory characteristics.

In order to solve this problem, as shown in Figure 2 C2 (: the position of the side ropes B and O is 1
The present inventors have proposed an attempt to reduce the phase distortion and reexcitation by biasing s8 in the direction of single-plane wave propagation (perpendicular to the direction of the oscillation).
Annual Electronic Communication Seikin Lecture 1 and Winter Collection 1'1-18 r? V:
Il! , 17MHg band 8AW-VIim174 for Shinyoko) J Showa S 6 JIF April), Figure 3 shows the same wave number amplitude characteristics of the filter with the structure shown in Figure 3, where Jl is given as 1 aldl/D. There is.

Kanyo Eiji, Haruka, the shoulder of the range, the characteristics are less rounded (but on the other hand, the -2 α5 dB near the left shoulder of the Haruka 1 range)
A relatively large amplitude ripple JJ occurs. This request kljt is unfavorable due to its characteristics and needs to be suppressed. Furthermore, if you look at Figure 3, you can see that the guaranteed attenuation on the high-frequency side of the stopband is smaller than that on the low-frequency side.
It is hoped that this point will also be improved.

The inventors conducted a detailed study on the causes of these amplitude ripples and the decrease in guaranteed attenuation, and found that these phenomena were due to the diffraction effect of surface acoustic waves.

11. The distance from the surface acoustic wave excitation source to the arrival point increases.11. The sum of the interdigital electrode crossing lengths of excitation IIA# becomes smaller, and the sum becomes larger.

Therefore, in FIG. 2, the diffraction of the elastic AM wave excited from the side beams B and O compared to the main beam is fused), and among them, the second beam 1).

From NSD 911] The far side...
:゛...1 The diffraction of the surface acoustic wave excited by the pump C appears much larger. And Th4i't: In the second wJ, the surface acoustic wave excited from the side rope 0 propagates away from the beam center axis of the surface acoustic wave excited from the main four-pump due to diffraction as shown by the arrow. By this, the 01st
Since the second transceiver tlli is outside the busbar IIm, it is considered that not everything is received at the second transceiver -'1''11.

In that case, one person was killed after taking into account the diffraction effect.
I had stains from the evening - when I performed the seal, the sll.
A decrease in the amplitude ripple and a decrease in the guaranteed attenuation on the high-frequency side of the first stop band were predicted, and it was confirmed that the results agreed well with the experimental results. That is, it has become clear that the deterioration of the properties observed in the first intended structure C2 is caused by the folding effect.

As a method of compensating for the diffraction effect, the length of the interdigital electrodes constituting the second transducer 11 can be adjusted by changing the length of the interdigital electrodes excited from the first transducer, 11. elastic table iii
The gun's beam axes 1:1 and 2 are symmetrically widened. However, this method has the disadvantage that the substrate size becomes slightly larger, leading to a significant increase in cost and a decrease in space 7 acme.

Therefore, it is an object of the present invention to move the violet lobes of the first transducer consisting of an apodized intermediate digital electrode from the main rope in a direction perpendicular to the direction of propagation of an acoustic acoustic wave (by a distance of 2 deviations f-2). Provides a surface acoustic wave device that compensates for the characteristic deterioration caused by the diffraction effect (=characteristic deterioration caused by the formation of a semiconductor substrate) without increasing the substrate size, and that can improve the characteristics and reduce the cost when forming a filter, etc. There are 62 things to do.

In this invention, the intersecting center axis of the regular interdigital electrodes constituting the second transducer is set to the beam center axis of the surface acoustic wave excited from the main leap of the first transducer. The direction of surface acoustic wave propagation is perpendicular to the two transducers and the second one of the side ropes of the first transducer is shifted in the direction of the position of the side rope of the first transducer; ;Accordingly, the surface acoustic wave propagation direction of the first transducer e@51! It is characterized by being shifted in the same direction as the direction of deviation of the intersecting center axis with respect to the mechanical center axis - the mechanical center axis i=.

According to Jin no Taka @Tsuka;, the surface acoustic wave excited from the side p-1 at a position gb far from the second transducer t of the first transducer and causing large diffraction also Since the signal is efficiently received by the transducer, the characteristic deterioration caused by the diffraction effect 1 is compensated for. 8.Furthermore, it is possible to prevent the surface acoustic waves excited from the side rays from propagating on the rasper in the first transducer to reduce the phase distortion of the surface acoustic waves. Is possible.

Furthermore, in this case, the intersecting central axes that constitute the second transducer and the first transducer! In order to make the mechanical central axis along the elastic lI box wave propagation direction perpendicular to the elastic AM wave propagation direction, when the diffraction effect is compensated by the conventional method of 9f, the substrate The increase in size is small.

Embodiments of the present invention will be described below with reference to the drawings.

4th WJ shows an embodiment of the present invention. In FIG. 0, 10 is a substrate capable of transmitting surface acoustic waves;
For example, a LINbO substrate with a 128°R displacement %Y cut is used. On this substrate 10, a first transducer 11 made of an apodized interdigital electrode and a second transducer 12 made of a regular type interdigital electrode are formed facing each other. 1st
As shown in Fig. 2, the transducer 1 has a main rope, and the main rope has two side ropes B and O at positions 1 and 1 shifted perpendicularly to the surface acoustic wave propagation direction. has. In addition, 13 Hata, 1'Jb is the busbar 41' 4 m' of transducer 11 of building I, J
4' b is □fJ+57, 1fL--! l”u”□'
z 、）っX／＜−”fah.

Here, bus bars JJb and J4b are formed on the same straight line in the surface acoustic wave propagation direction.

The busbar Jam, 14a is formed so that the elastic surface of the bus bar JJA is located on the line drawn by a distance IQ (: WL) in the direction perpendicular to the direction of liquid propagation. The beam center axis of the uniform plane wave excited from the main field of the first transducer 911, 4: On the other hand, the regular interdigital electrode constituting the second transducer 911 The intersection center axis is shifted by a distance WL/j perpendicular to the elastic surface liquid propagation direction and in the direction of the position of the nide helmet-10.
The distance WL is set to suppress the increase in the size of the board 1- as much as possible.
The elastic surface wrinkles of the Ftl-p0 and Wk8 are the minimum values that are received in the second Ftsunde-911.

In this way C=excited elastic reward wave device 7.: Then, the main
S gotta-□-The reward is the second trans-day tool as before-f
Arashiyuki 1 in ill; when received, tl;.

From the arrival point of the elastic 1lTj7iJ wave, it is excited from the side rope 0, which is a very strong excitation source, and undergoes large diffraction as shown by the arrow 1: The surface acoustic wave that spreads outward and propagates also Most public funds at t12
! Since r8 is reduced, it is possible to reduce the characteristic deterioration caused by the diffraction effect 6.

Moreover, since the second transducer 12q is located close to 62, the surface acoustic wave spreads due to the diffraction effect. , since the second transducer cannot be wiped, the intersection length of the regular interdigital electrodes constituting the second transducer is set to 42, which is about the beam center axis of the surface acoustic wave excited from the main rope. On the other hand, compared to the method of expanding symmetrically, the increase in the size of the substrate JO is only about half, and therefore the substrate material, which accounts for a large proportion of the price in a single surface acoustic wave device C, is reduced. Yo〕
, costs can be reduced significantly.

FIG.
In order not to pass through the top of the first totenmede-911
The mechanical center axis L along the elastic surface liquid propagation direction is the beam center axis of the elastic ms plane wave excited from the main pump, and the intersecting center axis of the IIHI transducer 11 is The deviation direction and opening direction Ii! Qr-biased S'. Calculate the amount of deviation between beam Il and l2 versus beam.

The partial capacitance of is incorrectly taken as WL/IL-=According to this lI example, the surface acoustic wave excited by the side rope 1as reaches the second tranmezzo -t1j1: ζ at the meeting where it arrives;
The ratio between the width of the electrode finger and the gap between the electrode fingers is the main
Since the force becomes stronger than that of the surface acoustic wave which is exclusively excited by the Bum and Side-11, there is an effect that the amount of phase due to disturbance of the wave front of one surface acoustic wave can be reduced.

The 6th cabinet was constructed by applying the structure of this example! This shows the same wave number amplitude characteristics of the VIB filter for MA transmission, #1 is 10 dB/D, and 11 is aIdl/D''e.As is clear from this figure, %5th lil! The amplitude ripple in the passband, which was observed in An ideal degree characteristic as a filter is obtained.It should be noted that the structure shown in FIG. 4 also provides similar characteristics, except that the phase distortion increases slightly.

The 7th WA shows still another embodiment of the present invention, in which the surface acoustic wave propagation directions of the side ropes B and O of the first transducer 11 are reversely placed in the vertical direction 1; However, the outside of the point plate in which the direction of deviation with respect to the axis L*eLa is reversed is the same as in Fig. S), and exactly the same effect as before can be obtained.

[Brief explanation of drawings]

Figures 1 and 2 are plan views of conventional surface acoustic wave devices;
Figure 3 is a diagram showing the frequency amplitude characteristics of the TV transmitter 11: Van filter for communication equipment by Kirizo in Figure 2.
WJ and FIG. 5 are plan views showing the configuration of one embodiment and other embodiments of the present invention, and No. 611 is a structural diagram of FIG. 5:
FIG. 2 is a plan view showing an embodiment of the second side of the V8B fin for the TV transmitter according to the present invention.
1...Second transducer, Ilm. 11b, 14m, 14k...Bus bar, M...Main rope, B, O...Side anchor-1゜Applicant's agent
Takehiko Suzue, Patent Attorney, 1゜1・,1:,・ □°・・・：5 ・,1(1・□'1 Spear 1, Fang, 2! 5 A 1, 3, published by MHI) Figure 4, Figure 5, Figure O, 6; """Stewtsu,. 3. Person making the amendment □ Relationship to the case Patent originator (sjy) Tokyo Shibaura Electric Co., Ltd. 4. Agent 5.1 Yoshiko Nara, “・□ 7. Contents of the amendment 1111 Specification Page 11111 Line 6~ lIT row r128
``°R propagation, Y cut'' is corrected as ``rotation Y cut, X propagation''.

Claims (1)

[Scope of Claims] 11) At least one main rope and a plurality of at least one main rope at positions deviated from the main rope by 12 in the vertical direction with respect to the surface acoustic wave propagation direction C. A first transducer consisting of two apodized interdigital electrodes is formed so as to form a side rope, and a second transducer consisting of regular interdigital electrodes is formed opposite the first transducer. A surface acoustic wave device forming a transducer (2, the above-mentioned 1+7)) Main rope of the transducer The central axis of the excited surface acoustic wave beam: On the other hand, The intersection center axis of the regular interdigital electrodes constituting the transducer is set perpendicular to the surface acoustic wave propagation direction and between the side ropes of the first transducer and the second tryst device. A surface acoustic wave device characterized in that the far side is shifted in the direction C. 121 Substrate cage for propagating surface acoustic waves: at least one main rope; A first transducer is formed of interdigital electrodes that have been subjected to nearpodization, and a second transducer that is made of regular interdigital electrodes is formed opposite to this first transducer. In the surface acoustic wave device (11'J!), the surface acoustic wave device (11'J!) formed by forming a surface acoustic wave The intersection central axes of the regular transverse-type impedance electrodes constituting the first transformer are perpendicular to the propagation direction and the second transformer is When the transducer is shifted in the direction of the position of the sidelobe farther from the transducer, the mechanical central axis along the surface acoustic wave propagation direction C of the first transducer is A surface acoustic wave device characterized in that the surface acoustic wave device is shifted from the central axis by 12 degrees in the same direction as the direction of deviation of the intersecting central axis.